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Was running fine until early Sunday morning, so I don't think it was due to an update.

Here are the steps I took to try to fix it:

Tried to reboot the server several times, didn't work.
Removed all mods and tried to reboot, didn't work.
Restarted the desktop computer that the server lives on, didn't change anything.
Verified the SE game files through the Steam App. It said all files were successfully verified.